Essential oil content in the leaves belonging to Eucalyptus camaldulensis from two different sites was determined and, their first antimicrobial effects on carbon mineralization of soil microorganisms were assessed. Eucalyptus leaves and soils were collected from Osmaniye and Adana cities of the Eastern Mediterranean region in Turkey. After determining the eucalyptol level in leaves by gas chromatography-mass spectrometry, soils were mixed with powdered leaves (L) and pure eucalyptol (E) based on their C contents at quarter (Q), half (H) and same (S) doses of soil organic C level. Carbon mineralization of all soils was determined by CO2 respiration method for 30 d (28 degrees C, 80% field capacity). Our results showed that eucalyptol (50.0%) of obtained essential oil from Eucalyptus camaldulensis leaves planted in Osmaniye was significantly higher than Adana (23.5%) by GC-MS analysis (p = 0.000). All of eucalyptol doses added to Adana soil significantly decreased carbon mineralization while Osmaniye soil did not affect from different eucalyptol doses during the all incubation periods. LQ and LH doses of Eucalyptus leaves added to Adana soil stimulated microbial respiration except of LS dose. This result might explain that soil microorganisms used Eucalyptus leaves as C source at LQ and LH doses of Adana soil. It may be concluded that site difference, organic matter amounts, different eucalyptol doses affected C mineralization and its ratio into the 30 days.